Light beam generators for generating light having a predetermined phase distribution on a beam cross section of light described in Patent Document 1 and Non-Patent Documents 1 to 7 are known. Light beam generators described in these documents generate Laguerre-Gaussian Mode light (hereinafter referred to as “LG mode light”) in which a phase changes along a circumferential direction on a beam cross section of light. This LG mode light is expected to be used for laser optical tweezers, quantum calculations and quantum communications, now a focus of attention in the fields of optics and physics.    [Patent Document 1] Japanese Translation of International Application No. 2001-523396    [Non-Patent Document 1] J. Arlt, et al., Journal of Modern Optics, Vol. 45, No. 6, pp. 1231-1237 (1998).    [Non-Patent Document 2] D. G Grier, Nature, Vol. 424, pp. 810-816 (2003).    [Non-Patent Document 3] M. W. Beijersbergen, et al., Optics Communications, Vol. 112, pp. 321-327 (1994).    [Non-Patent Document 4] K. Sueda, et al., Optics Express, Vol. 12, No. 15, pp. 3548-3553 (2004).    [Non-Patent Document 5] N. R. Heckenberg, et al., Optics Letters, Vol. 17, No. 3, pp. 221-223 (1992).    [Non-Patent Document 6] N. R. Heckenberg, et al., Optical and Quantum Electronics, Vol. 24, No. 24, pp. 155-166 (1992).    [Non-Patent Document 7] J. Arlt, T. Hitomi, K. Dholakia, Applied Physics, B, Vol. 71, pp. 549-554 (2000).